Method and device for executing HARQ in TDD-based wireless communication system

ABSTRACT

Provided are a method and a device for executing a hybrid automatic repeat request (HARQ) of a terminal in a time division duplex (TDD)-based wireless communication system. The method comprises the steps of: receiving an uplink grant for a first subframe of a second serving cell through a first serving cell; transmitting uplink data in the first subframe on the basis of the uplink grant; receiving an acknowledgement/not-acknowledgement (ACK/NACK) for the uplink data through the first serving cell; and, when the ACK/NACK signal is a NACK, transmitting a retransmission data for the uplink data in a second subframe of the second serving cell.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT/KR2012/002038 filed onMar. 21, 2012, which claims priority under 35 U.S.C. 119(e) to U.S.Provisional Application No. 61/454,975 filed on Mar. 21, 2011, U.S.Provisional Application No. 61/470,499 filed on Apr. 1, 2011, U.S.Provisional Application No. 61/587,082 filed on Jan. 16, 2012, and U.S.Provisional Application No. 61/594,384 filed on Feb. 3, 2012, all ofwhich are hereby expressly incorporated by reference into the presentapplication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communication, and, moreparticularly, to a method and apparatus for performing a hybridautomatic repeat request (HARQ) in a wireless communication system basedon Time Division Duplex (TDD).

2. Related Art

Long Term Evolution (LTE) based on 3^(rd) Generation Partnership Project(3GPP) Technical Specification (TS) Release 8 is the leadingnext-generation mobile communication standard.

As disclosed in 3GPP TS 36.211 V8.7.0 (2009-05) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, in LTE, a physical channel can be divided into a PhysicalDownlink Shared Channel (PDSCH) and a Physical Downlink Control Channel(PDCCH), that is, downlink channels, and a Physical Uplink SharedChannel (PUSCH) and a Physical Uplink Control Channel (PUCCH), that is,uplink channels.

A PUCCH is an uplink control channel used to send uplink controlinformation, such as a Hybrid Automatic Repeat reQuest (HARQ), anacknowledgement/not-acknowledgement (ACK/NACK) signal, a Channel QualityIndicator (CQI), and a Scheduling Request (SR).

Meanwhile, 3GPP LTE-Advanced (A) that is the evolution of 3GPP LTE is inprogress. Technology introduced into 3GPP LTE-A includes a carrieraggregation.

A carrier aggregation uses a plurality of component carriers. Acomponent carrier is defined by the center frequency and a bandwidth.One downlink component carrier or a pair of an uplink component carrierand a downlink component carrier correspond to one cell. It can be saidthat a terminal being served using a plurality of downlink componentcarriers is being served from a plurality of serving cells.

In a Time Division Duplex (TDD) system, the same frequency is used inuplink and downlink. Accordingly, one or more DL subframes areassociated with an UL subframe. The “association” means thattransmission/reception in the DL subframe is associated withtransmission/reception in the UL subframe. For example, when a transportblock is received in a plurality of DL subframes, a terminal sends HARQACK/NACK (hereinafter referred to as ACK/NACK) for the transport blockin an UL subframe associated with a plurality of DL subframes. Here, aminimum time is necessary to send the ACK/NACK. This is because the timetaken to process the transport block and the time taken to process theACK/NACK are necessary.

Meanwhile, a plurality of serving cells can be introduced into a TDDsystem. That is, a plurality of serving cells can be assigned to aterminal. In this case, in the prior art, it was assumed that the sameuplink-downlink (UL-DL) configuration was used in all the serving cells.The UL-DL configuration is information indicating whether each subframewithin a radio frame used in TDD is an UL subframe or a DL subframe. Inthe next-generation wireless communication system, however, to usedifferent UL-DL configurations in serving cells is also taken intoconsideration. In this case, how an HARQ will be performed using whatmethod is problematic.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and apparatusfor performing an HARQ in a wireless communication system based on TimeDivision Duplex (TDD).

In an aspect, there is provided a method of performing, by userequipment to which a plurality of serving cells based on Time DivisionDuplex (TDD) has been allocated, a hybrid automatic repeat request(HARQ). The method includes the steps of receiving an uplink grant for afirst subframe of a second serving cell through a first serving cell;sending UL data in the first subframe based on the uplink grant;receiving an acknowledgment/not-acknowledgement (ACK/NACK) signal forthe UL data through the first serving cell; and sending retransmissiondata for the UL data in a second subframe of the second serving cell ifthe ACK/NACK signal is NACK, wherein the first serving cell and thesecond serving cell use different UL-DL configurations, and the UL-DLconfiguration is information on which each subframe within a TDD frameis configured as an UL subframe or a DL subframe.

The first subframe and the second subframe may be subframes that formthe same HARQ process.

An HARQ period indicative of a time interval from the first subframe toa subframe right before the second subframe may be a whole number timesthen HARQ period in the case where one serving cell is allocated to theuser equipment.

The first subframe and the second subframe may be subframes configuredas UL subframes according to the UL-DL configuration used in the secondserving cell.

The user equipment may do not search an UL subframe of the secondserving cell, placed between the first subframe and the second subframe,for an uplink grant.

The first serving cell may be a primary cell through which the userequipment performs an initial connection establishment procedure or aconnection reestablishment procedure along with a base station.

The second serving cell may be a secondary cell additionally allocatedto the user equipment in addition to the primary cell.

In the first serving cell and the second serving cell, independent HARQprocesses having a number identical with the number of UL subframes ofthe second serving cell which are placed in an interval between thefirst subframe and a subframe right before the second subframe may beperformed.

In the first serving cell and the second serving cell, independent HARQprocesses having a number identical with the number of valid ULsubframes of the second serving cell which are placed in an intervalbetween the first subframe and a subframe right before the secondsubframe may be performed.

The valid UL subframe may be an UL subframe in which the transmission ofthe UL data is possible and the transmission of an uplink grantcorresponding to the UL data transmission is possible in a subframe inwhich the uplink grant is transmitted.

In another aspect, there is provided a method of performing, by userequipment to which a plurality of serving cells based on Time DivisionDuplex (TDD) has been allocated, a hybrid automatic repeat request(HARQ). The method includes the steps of receiving a grant for a firstsubframe of a second serving cell through a first serving cell; sendingdata in the first subframe based on the grant; and receiving anacknowledgment/not-acknowledgement (ACK/NACK) signal for the datathrough the first serving cell, wherein the first serving cell and thesecond serving cell use different UL-DL configurations, and the UL-DLconfiguration is information on which each subframe within a TDD frameis configured as an UL subframe or a DL subframe.

A first UL-DL configuration used in the first serving cell or a secondUL-DL configuration used in the second serving cell may have the sameregression period of an HARQ process.

The first UL-DL configuration and the second UL-DL configuration mayhave the same DL-UL switch-point periodicity.

In yet another aspect, there is provided a method of performing, by userequipment to which a plurality of serving cells based on Time DivisionDuplex (TDD) has been allocated, a hybrid automatic repeat request(HARQ). The method includes the steps of receiving an uplink grant for afirst subframe of a second serving cell through a first serving cell;sending first UL data in the first subframe based on the uplink grant;receiving an uplink grant for a second subframe of the second servingcell in the first serving cell, the uplink grant for the second subframecomprising information indicative of whether or not the first UL data isto be retransmitted; and sending second UL data in the second subframebased on the uplink grant for the second subframe, wherein the firstserving cell and the second serving cell use different UL-DLconfigurations, and the UL-DL configuration is information on which eachsubframe within a TDD frame is configured as an UL subframe or a DLsubframe, if the information indicative of whether or not the UL data isto be retransmitted indicates retransmission, the second UL data isretransmission data of the first UL data, and if the informationindicative of whether or not the UL data is to be retransmittedindicates new transmission, the second UL data is new UL data, and asubframe of the first serving cell in which the uplink grant for thesecond subframe is received does not include physical hybrid-ARQindicator channel (PHICH) resources.

In the case of the subframe in which the uplink grant for the secondsubframe is received in the first serving cell, the user equipment maydecode only the uplink grant for the second subframe without attemptingto receive a physical hybrid-ARQ indicator channel (PHICH).

UE provided in further yet another aspect includes a Radio Frequency(RF) unit transmitting and receiving radio signals and a processorconnected with the RF unit, wherein the processor receives an uplinkgrant for a first subframe of a second serving cell through a firstserving cell, sends UL data in the first subframe based on the uplinkgrant, receives an acknowledgment/not-acknowledgement (ACK/NACK) signalfor the UL data through the first serving cell, and sends retransmissiondata for the UL data in a second subframe of the second serving cell ifthe ACK/NACK signal is NACK, wherein the first serving cell and thesecond serving cell use different UL-DL configurations, and the UL-DLconfiguration is information on which each subframe within a TDD frameis configured as an UL subframe or a DL subframe, and an HARQ periodindicative of an interval between the first subframe and the secondsubframe is a whole number times an HARQ period in the case where oneserving cell is allocated.

A synchronous HARQ can be performed even when each serving cell uses adifferent UL-DL configuration in a Time Division Duplex (TDD) systemincluding a plurality of serving cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of a radio frame.

FIG. 2 shows the structure of a TDD radio frame.

FIG. 3 shows an example of a resource grid for one downlink slot.

FIG. 4 shows the structure of a DL subframe.

FIG. 5 shows the structure of an UL subframe.

FIG. 6 shows the channel structure of a PUCCH format 1b in a normal CP.

FIG. 7 shows the channel structure of PUCCH formats 2/2a/2b in a normalCP.

FIG. 8 illustrates an Enhanced (E)-PUCCH format based onblock-spreading.

FIG. 9 shows an example of a DL HARQ.

FIG. 10 shows a synchronization HARQ process in FDD.

FIGS. 11 to 17 show examples of k, j, r, and k′ values according toUL-DL configurations (refer to Table 1) of a TDD frame and subframenumbers.

FIG. 18 is a comparison example of a single carrier system and a carrieraggregation system.

FIG. 19 shows an example in which each serving cell uses a differentUL-DL configuration.

FIG. 20 shows a problem in a process of performing a synchronous HARQwhen each serving cell uses a different UL-DL configuration.

FIG. 21 shows a process of performing a synchronous HARQ when eachserving cell uses a different UL-DL configuration.

FIG. 22 shows a process of performing a synchronous HARQ when eachserving cell uses a different UL-DL configuration.

FIG. 23 shows HARQ timing when the method of FIG. 22 is used.

FIGS. 24 and 25 show examples in which the number of HARQ processes ismade identical with an HARQ process period by equally distributing ULgrants and PHICH transmission time points.

FIG. 26 shows a problem that may occur when serving cells in which anUL-DL configuration having the same j+r value is used are aggregated.

FIG. 27 shows a method of changing the number of HARQ processes.

FIG. 28 shows the method 4).

FIG. 29 shows a method of performing an HARQ according to the method 5).

FIG. 30 shows an example in which the present invention is applied to asingle serving cell.

FIG. 31 shows HARQ timing according to subframe bundling in FDD.

FIG. 32 is a block diagram showing a wireless apparatus in which anembodiment of the present invention is implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

User Equipment (UE) can be fixed or can have mobility. UE can also becalled another term, such as a Mobile Station (MS), a Mobile Terminal(MT), a User Terminal (UT), a Subscriber Station (SS), a wirelessdevice, a Personal Digital Assistant (PDA), a wireless modem, or ahandheld device.

The BS commonly refers to a fixed station that communicates with UE. TheBS can also be called another tem, such as an evolved-NodeB (eNodeB), aBase Transceiver System (BTS), or an access point.

Communication from a BS to UE is called downlink (DL), and communicationfrom UE to a BS is called uplink (UL). A wireless communication systemincluding a BS and UE can be a Time Division Duplex (TDD) system or aFrequency Division Duplex (FDD) system. A TDD system is a wirelesscommunication system that performs UL and DL transmission/receptionusing different times in the same frequency band. An FDD system is awireless communication system that enables UL and DLtransmission/reception at the same time using different frequency bands.A wireless communication system can perform communication using radioframes.

FIG. 1 shows the structure of a radio frame.

The radio frame includes 10 subframes, and one subframe includes twoconsecutive slots. The slots within the radio frame are assigned indices0-19. The time that is taken for one subframe to be transmitted iscalled a Transmission Time Interval (TTI). A TTI can be a minimumscheduling unit. For example, the length of one subframe can be 1 ms,and the length of one slot can be 0.5 ms. Such a radio frame can be usedin FDD. In this case, this radio frame is called an FDD frame.

FIG. 2 shows the structure of a TDD radio frame.

Referring to FIG. 2, in the TDD radio frame (hereinafter referred to asa TDD frame), subframes having an index #1 and an index #6 are calledspecial subframes, and the subframe includes a Downlink Pilot Time Slot(DwPTS), a Guard Period (GP), and an Uplink Pilot Time Slot (UpPTS). TheDwPTS is used in initial cell search, synchronization, or channelestimation in UE. The UpPTS is used for channel estimation in a BS andfor the uplink transmission synchronization of UE. The GP is an intervalin which interference occurring in UL due to the multi-path delay of aDL signal between UL and DL is removed.

In TDD, a downlink (DL) subframe and an uplink (UL) subframe coexist inone radio frame. Table 1 shows an example of the UL-DL configuration ofa radio frame.

TABLE 1 Uplink-downlink Downlink-to-Uplink Subframe number nconfiguration Switch-point periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S UU U D S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10ms  D S U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D DD D D D D 6 5 ms D S U U U D S U U D

In Table 1, ‘D’ indicates a DL subframe, ‘U’ indicates an UL subframe,and ‘S’ indicates a special subframe. When an UL-DL configuration isreceived from a BS, UE can be aware whether each subframe in a radioframe is a DL subframe or an UL subframe. Hereinafter, reference can bemade to Table 1 for an UL-DL configuration N (N is any one of 0 to 6).

FIG. 3 shows an example of a resource grid for one downlink slot.

Referring to FIG. 3, the downlink slot includes a plurality ofOrthogonal Frequency Division Multiplexing (OFDM) symbol in the timedomain and includes N_(RB) Resource Blocks (RBs) in the frequencydomain. The RBs includes one slot in the time domain and a plurality ofconsecutive subcarrier in the frequency domain in a resource allocationunit. The number of RBs N_(RB) included in the downlink slot depends ona downlink transmission bandwidth N^(DL) configured in a cell. Forexample, in an LTE system, the N_(RB) can be any one of 6 to 110. Anuplink slot can have the same structure as the downlink slot.

Each element on the resource grid is called a Resource Element (RE). TheRE on the resource grid can be identified by an index pair (k,l) withina slot. Here, k (k=0, . . . , N_(RB)×12−1) is a subcarrier index withinthe frequency domain, and l (l=0, . . . , 6) is an OFDM symbol indexwithin the time domain.

Although 7×12 REs including 7 OFDM symbols in the time domain and 12subcarrier in the frequency domain have been illustrated as beingincluded in one RB in FIG. 3, the number of OFDM symbols and the numberof subcarriers within an RB are not limited thereto. The number of OFDMsymbols and the number of subcarriers can be changed in various waysdepending on the length of a CP, frequency spacing, etc. In one OFDMsymbol, one of 128, 256, 512, 1024, 1536, and 2048 can be selected andused as the number of subcarriers.

FIG. 4 shows the structure of a DL subframe.

Referring to FIG. 4, a downlink (DL) subframe is divided into a controlregion and a data region in the time domain. The control region includesa maximum of former 3 (4 according to circumstances) OFDM symbols of afirst slot within a subframe, but the number of OFDM symbols included inthe control region can be varied. A control channel different from aphysical downlink control channel (PDCCH) is allocated to the controlregion, and a physical downlink shared channel (PDSCH) is allocated tothe data region.

As disclosed in 3GPP TS 36.211 V8.7.0, in 3GPP LTE, physical channelscan be divided into a physical downlink shared channel (PDSCH) and aphysical uplink shared channel (PUSCH), that is, data channels, and aphysical downlink control channel (PDCCH), a physical control formatindicator channel (PCFICH), a physical hybrid-ARQ indicator channel(PHICH), and a physical uplink control channel (PUCCH), that is, controlchannels.

A PCFICH that is transmitted in the first OFDM symbol of a subframecarries a Control Format Indicator (CFI) regarding the number of OFDMsymbols (i.e., the size of a control region) that are used to sendcontrol channels within the subframe. UE first receives a CFI on aPCFICH and then monitors PDCCHs. Unlike in a PDCCH, a PCFICH is notsubject to blind decoding, but is transmitted through the fixed PCFICHresources of a subframe.

A PHICH carries a positive-acknowledgement(ACK)/negative-acknowledgement (NACK) signal for an uplink HybridAutomatic Repeat reQuest (HARQ). An ACK/NACK signal for uplink (UL) dataon a PUSCH which is transmitted by UE is transmitted on a PHICH.

A physical broadcast channel (PBCH) is transmitted in the former 4 OFDMsymbols of a second slot within the first subframe of a radio frame. ThePBCH carries system information that is essential for UE to communicatewith a BS, and system information transmitted through a PBCH is called aMaster Information Block (MIB). In contrast, system informationtransmitted on a PDSCH indicated by a PDCCH is called a SystemInformation Block (SIB).

Control information transmitted through a PDCCH is called DownlinkControl Information (DCI). DCI can include the resource allocation of aPDSCH (this is also called a DL grant), the resource allocation of aPUSCH (this is also called an UL grant), a set of transmit power controlcommands for individual MSs within a specific UE group and/or theactivation of a Voice over Internet Protocol (VoIP).

FIG. 5 shows the structure of an UL subframe.

Referring to FIG. 5, the UL subframe can be divided into a controlregion to which a physical uplink control channel (PUCCH) for carryinguplink control information is allocated and a data region to which aphysical uplink shared channel (PUSCH) for carrying user data isallocated in the frequency domain.

A PUCCH is allocated with an RB pair in a subframe. RBs that belong toan RB pair occupy different subcarriers in a first slot and a secondslot. An RB pair has the same RB index m.

In accordance with 3GPP TS 36.211 V8.7.0, a PUCCH supports multipleformats. A PUCCH having a different number of bits in each subframe canbe used according to a modulation scheme that is dependent on a PUCCHformat.

Table 2 below shows an example of modulation schemes and the number ofbits per subframe according to PUCCH formats.

TABLE 2 PUCCH format Modulation scheme number of bits per subframe 1 N/AN/A 1a BPSK 1 1b QPSK 2 2 QPSK 20 2a QPSK + BPSK 21 2b QPSK + QPSK 22

The PUCCH format 1 is used to send a Scheduling Request (SR), the PUCCHformats 1a/1b are used to send an ACK/NACK signal for an HARQ, the PUCCHformat 2 is used to send a CQI, and the PUCCH formats 2a/2b are used tosend a CQI and an ACK/NACK signal at the same time. When only anACK/NACK signal is transmitted in a subframe, the PUCCH formats 1a/1bare used. When only an SR is transmitted, the PUCCH format 1 is used.When an SR and an ACK/NACK signal are transmitted at the same time, thePUCCH format 1 is used. In this case, the ACK/NACK signal is modulatedinto resources allocated to the SR and is then transmitted.

All the PUCCH formats use the Cyclic Shift (CS) of a sequence in eachOFDM symbol. A CS sequence is generated by cyclically shifting a basesequence by a specific CS amount. The specific CS amount is indicated bya CS index.

An example in which a base sequence r_(u)(n) has been defined is thesame as the following equation.r _(u)(n)=e ^(jb(n)π/4)  [Equation 1]

Here, u is a root index, n is an element index wherein 0≦n≦N−1, and N isthe length of the base sequence. b(n) is defined in section 5.5 of 3GPPTS 36.211 V8.7.0.

The length of a sequence is the same as the number of elements includedin the sequence. U can be determined by a cell identifier (ID), a slotnumber within a radio frame, etc. Assuming that a base sequence ismapped to one resource block in the frequency domain, the length N ofthe base sequence becomes 12 because one resource block includes 12subcarriers. A different base sequence is defined depending on adifferent root index.

A CS sequence r(n, I_(cs)) can be generated by cyclically shifting thebase sequence r(n) as in Equation 2.

$\begin{matrix}{{{r\left( {n,I_{cs}} \right)} = {{r(n)} \cdot {\exp\left( \frac{{j2\pi}\; I_{cs}n}{N} \right)}}},{0 \leq I_{cs} \leq {N - 1}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Here, I_(cs) is a CS index indicative of a CS amount (0≦I_(cs)≦N−1).

An available CS index of a base sequence refers to a CS index that canbe derived from the base sequence according to a CS interval. Forexample, the length of a base sequence is 12 and a CS interval is 1, atotal number of available CS indices of the base sequence becomes 12.Or, if the length of a base sequence is 12 and a CS interval is 2, atotal number of available CS indices of the base sequence becomes 6.

FIG. 6 shows the channel structure of the PUCCH format 1b in a normalCP.

One slot includes 7 OFDM symbols, the 3 OFDM symbols become ReferenceSignal (RS) OFDM symbols for a reference signal, and the 4 OFDM symbolsbecome data OFDM symbols for an ACK/NACK signal.

In the PUCCH format 1b, a modulation symbol d(0) is generated byperforming Quadrature Phase Shift Keying (QPSK) modulation on an encoded2-bit ACK/NACK signal.

A CS index I_(cs) can vary depending on a slot number ‘n_(s)’ within aradio frame and/or a symbol index ‘1’ within a slot.

In a normal CP, 4 data OFDM symbols for sending an ACK/NACK signal arepresent in one slot. It is assumed that corresponding CS indices inrespective data OFDM symbols are I_(cs0), I_(cs1), I_(cs2), and I_(cs3).

The modulation symbol d(0) is spread into a CS sequence r(n,I_(cs)).Assuming that a 1-dimensional spread sequence corresponding to an(i+1)^(th) OFDM symbol is m(i) in a slot,

{m(0), m(1), m(2), m(3)}={d(0)r(n,I_(cs0)), d(0)r(n,I_(cs1)),d(0)r(n,I_(cs2)), d(0)r(n,I_(cs3))} can be obtained.

In order to increase a UE capacity, the 1-dimensional spread sequencecan be spread using an orthogonal sequence. The following sequence isused as an orthogonal sequence w_(i)(k) (i is a sequence index, 0≦k≦K−1)wherein a spreading factor K=4.

TABLE 3 Index (i) [w_(i)(0), w_(i)(1), w_(i)(2), w_(i)(3)] 0 [+1, +1,+1, +1] 1 [+1, −1, +1, −1] 2 [+1, −1, −1, +1]

The following sequence is used as an orthogonal sequence w_(i)(k) (i isa sequence index, 0≦k≦K−1) wherein a spreading factor K=3.

TABLE 4 Index (i) [w_(i)(0), w_(i)(1), w_(i)(2)] 0 [+1, +1, +1] 1 [+1,e^(j2π/3), e^(j4π/3)] 2 [+1, e^(j4π/3), e^(j2π/3)]

A different spreading factor can be used in each slot.

Accordingly, assuming that a specific orthogonal sequence index i isgiven, 2-dimensional spread sequences {s(0), s(1), s(2), s(3)} can beexpressed as follows.

{s(0), s(1), s(2), s(3)}={w_(i)(0)m(0), w_(i)(1)m(1), w_(i)(2)m(2),w_(i)(3)m(3)}

The 2-dimensional spread sequences {s(0), s(1), s(2), s(3)} are subjectto IFFT and then transmitted in a corresponding OFDM symbol.Accordingly, an ACK/NACK signal is transmitted on a PUCCH.

A reference signal having the PUCCH format 1b is also transmitted byspreading the reference signal into an orthogonal sequence aftercyclically shifting a base sequence r(n). Assuming that CS indicescorresponding to 3 RS OFDM symbols are I_(cs4), I_(cs5), and I_(cs6), 3CS sequences r(n,I_(cs4)), r(n,I_(cs5)), r(n,I_(cs6)) can be obtained.The 3 CS sequences are spread into an orthogonal sequence w^(RS) _(i)(k)wherein K=3.

An orthogonal sequence index i, a CS index I_(cs), and an RB index m areparameters necessary to configure a PUCCH and are also resources used toclassify PUCCHs (or MSs). If the number of available CSs is 12 and thenumber of available orthogonal sequence indices is 3, a PUCCH for atotal of 36 MSs can be multiplexed with one RB.

In 3GPP LTE, a resource index n⁽¹⁾ _(PUCCH) is defined so that UE canobtain the three parameters for configuring a PUCCH. The resource indexn⁽¹⁾ _(PUCCH)=n_(CCE)+N⁽¹⁾ _(PUCCH), wherein n_(CCE) is the number ofthe first CCE used to send a corresponding PDCCH (i.e., PDCCH includingthe allocation of DL resources used to received downlink datacorresponding to an ACK/NACK signal), and N⁽¹⁾ _(PUCCH) is a parameterthat is informed of UE by a BS through a higher layer message.

Time, frequency, and code resources used to send an ACK/NACK signal arecalled ACK/NACK resources or PUCCH resources. As described above, anindex of ACK/NACK resources (called an ACK/NACK resource index or PUCCHindex) used to send an ACK/NACK signal on a PUCCH can be represented asat least one of an orthogonal sequence index i, a CS index I_(cs), an RBindex m, and an index for calculating the 3 indices. ACK/NACK resourcescan include at least one of an orthogonal sequence, a CS, a resourceblock, and a combination of them.

FIG. 7 shows the channel structure of the PUCCH formats 2/2a/2b in anormal CP.

Referring to FIG. 7, in a normal CP, OFDM symbols 1 and 5 (i.e., secondand sixth OFDM symbols) are used to send a demodulation reference signal(DM RS), that is, an uplink reference signal, and the remaining OFDMsymbols are used to send a CQI. In the case of an extended CP, an OFDMsymbol 3 (fourth symbol) is used for a DM RS.

10 CQI information bits can be subject to channel coding at a ½ coderate, for example, thus becoming 20 coded bits. Reed-Muller code can beused in the channel coding. Next, the 20 coded bits are scramble andthen subject to QPSK constellation mapping, thereby generating a QPSKmodulation symbol (d(0) to d(4) in a slot 0). Each QPSK modulationsymbol is modulated in a cyclic shift of a base RS sequence ‘r(n)’having a length of 12, subject to IFFT, and then transmitted in each of10 SC-FDMA symbols within a subframe. Uniformly spaced 12 CSs enable 12different MSs to be orthogonally multiplexed in the same PUCCH RB. Abase RS sequence ‘r(n)’ having a length of 12 can be used as a DM RSsequence applied to OFDM symbols 1 and 5.

FIG. 8 illustrates an Enhanced (E)-PUCCH format based onblock-spreading.

An E-PUCCH format is also called the PUCCH format 3.

Referring to FIG. 8, the E-PUCCH format is a PUCCH format that uses ablock-spreading scheme. The block-spreading scheme means a method ofmultiplexing a modulation symbol sequence that has been modulated frommulti-bit ACK/NACK using block-spreading code. An SC-FDMA scheme can beused in the block-spreading scheme. Here, the SC-FDMA scheme means atransmission method of performing IFFT after DFT spreading.

An E-PUCCH format is transmitted in such a manner that a symbol sequence(e.g., ACK/NACK symbol sequence) is spread in the time domain by way ofblock-spreading code. Orthogonal Cover Code (OCC) can be used as theblock-spreading code. The control signals of several MSs can bemultiplexed by the block-spreading code. In the PUCCH format 2, onesymbol sequence is transmitted in the time domain, and UE multiplexingis performed using the cyclic shift of a Constant Amplitude ZeroAuto-Correlation (CAZAC) sequence. In contrast, in the E-PUCCH format, asymbol sequence including one or more symbols is transmitted in thefrequency domain of each data symbol, the symbol sequence is spread inthe time domain by way of block-spreading code, and UE multiplexing isperformed. An example in which 2 RS symbols are used in one slot hasbeen illustrated in FIG. 8, but the present invention is not limitedthereto. 3 RS symbols can be used, and OCC in which a spreading factorvalue is 4 may be used. An RS symbol can be generated from a CAZACsequence having a specific CS and can be transmitted in such a mannerthat a plurality of RS symbols in the time domain has been multiplied byspecific OCC.

ACK/NACK transmission for HARQ in 3GPP LTE Time Division Duplex (TDD) isdescribed below.

In TDD, unlike in a Frequency Division Duplex (FDD), a DL subframe andan UL subframe coexist in one radio frame. In general, the number of ULsubframes is smaller than that of DL subframes. Accordingly, inpreparation for a case where UL subframes for sending an ACK/NACK signalare not sufficient, a plurality of ACK/NACK signals for DL transportblocks received in a plurality of DL subframes is transmitted in one ULsubframe.

In accordance with section 10.1 of 3GPP TS 36.213 V8.7.0 (2009 May), twoACK/NACK modes: ACK/NACK bundling and ACK/NACK multiplexing areinitiated.

In ACK/NACK bundling, UE sends ACK if it has successfully decoded allreceived PDSCHs (i.e., DL transport blocks) and sends NACK in othercases. To this end, ACK or NACKs for each PDSCH are compressed throughlogical AND operations.

ACK/NACK multiplexing is also called ACK/NACK channel selection (orsimply channel selection). In accordance with ACK/NACK multiplexing, UEselects one of a plurality of PUCCH resources and sends ACK/NACK.

Table below shows DL subframes n-k associated with an UL subframe naccording to an UL-DL configuration in 3GPP LTE, wherein kεK and M isthe number of elements of a set K.

TABLE 5 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 — — 6 — 4 —— 6 — 4 1 — — 7, 6 4 — — — 7, 6 4 — 2 — — 8, 7, 4, 6 — — — — 8, 7, 4, 6— — 3 — — 7, 6, 11 6, 5 5, 4 — — — — — 4 — — 12, 8, 7, 11 6, 5, 4, 7 — —— — — — 5 — — 13, 12, 9, 8, 7, 5, — — — — — — — 4, 11, 6 6 — — 7 7 5 — —7 7 —

It is assumed that M DL subframes are associated with the UL subframe nand, for example, M=3. In this case, UE can obtain 3 PUCCH resourcesn⁽¹⁾ _(PUCCH,0), n⁽¹⁾ _(PUCCH,1), and n⁽¹⁾ _(PUCCH,2) because it canreceive 3 PDCCHs from 3 DL subframes. In this case, an example ofACK/NACK channel selection is the same as the following table.

TABLE 6 HARQ-ACK(0), HARQ-ACK(1), HARQ- ACK(2) n⁽¹⁾ _(PUCCH) b(0), b(1)ACK, ACK, ACK n⁽¹⁾ _(PUCCH, 2) 1, 1 ACK, ACK, NACK/DTX n⁽¹⁾ _(PUCCH, 1)1, 1 ACK, NACK/DTX, ACK n⁽¹⁾ _(PUCCH, 0) 1, 1 ACK, NACK/DTX, NACK/DTXn⁽¹⁾ _(PUCCH, 0) 0, 1 NACK/DTX, ACK, ACK n⁽¹⁾ _(PUCCH, 2) 1, 0 NACK/DTX,ACK, NACK/DTX n⁽¹⁾ _(PUCCH, 1) 0, 0 NACK/DTX, NACK/DTX, ACK n⁽¹⁾_(PUCCH, 2) 0, 0 DTX, DTX, NACK n⁽¹⁾ _(PUCCH, 2) 0, 1 DTX, NACK,NACK/DTX n⁽¹⁾ _(PUCCH, 1) 1, 0 NACK, NACK/DTX, NACK/DTX n⁽¹⁾ _(PUCCH, 0)1, 0 DTX, DTX, DTX N/A N/A

In the above table, HARQ-ACK(i) indicates ACK/NACK for an i^(th) DLsubframe of M DL subframes. Discontinuous transmission (DTX) means thata DL transport block has not been received on a PDSCH in a correspondingDL subframe or that a corresponding PDCCH has not been detected. Inaccordance with Table 6, 3 PUCCH resources n⁽¹⁾ _(PUCCH,0), n⁽¹⁾_(PUCCH,1), and n⁽¹⁾ _(PUCCH,2) are present, and b(0), b(1) are two bitstransmitted using a selected PUCCH.

For example, when UE successfully receives all 3 DL transport blocks in3 DL subframes, the UE performs QPSK modulation on bits (1,1) using n⁽¹⁾_(PUCCH,2) and sends them on a PUCCH. If UE fails in decoding a DLtransport block in a first (i=0) DL subframe, but succeeds in decodingthe remaining transport blocks, the UE sends bits (1,0) on a PUCCH usingn⁽¹⁾ _(PUCCH,2). That is, in the existing PUCCH format 1b, only ACK/NACKof 2 bits can be transmitted. In channel selection, however, allocatedPUCCH resources are linked to an actual ACK/NACK signal in order toindicate more ACK/NACK states.

In ACK/NACK channel selection, if at least one ACK is present, NACK andDTX are coupled. This is because all ACK/NACK states cannot berepresented by a combination of reserved PUCCH resources and a QPSKsymbol. If ACK is not present, however, DTX is decoupled from NACK.

The above-described ACK/NACK bundling and ACK/NACK multiplexing can beapplied in the case where one serving cell has been configured in UE inTDD.

For example, it is assumed that one serving cell has been configured(i.e., only a primary cell is configured) in UE in TDD, ACK/NACKbundling or ACK/NACK multiplexing is used, and M=1. That is, it isassumed that one DL subframe is associated with one UL subframe.

1) UE sends ACK/NACK in a subframe n if the UE detects a PDSCH indicatedby a corresponding PDCCH in a subframe n−k of a primary cell or detectsa Semi-Persistent Scheduling (SPS) release PDCCH. In LTE, a BS caninform UE that semi-persistent transmission and reception are performedin what subframes through a higher layer signal, such as Radio ResourceControl (RRC). Parameters given by the higher layer signal can be, forexample, the periodicity of a subframe and an offset value. When the UEreceives the activation or release signal of SPS transmission through aPDCCH after recognizing semi-persistent transmission through the RRCsignaling, the UE performs or releases SPS PDSCH reception or SPS PUSCHtransmission. That is, the UE does not immediately perform SPStransmission/reception although SPS scheduling is allocated theretothrough the RRC signaling, but when an activation or release signal isreceived through a PDCCH, performs SPS transmission/reception in asubframe that corresponds to frequency resources (resource block)according to the allocation of the resource block designated by thePDCCH, modulation according to MCS information, subframe periodicityallocated through the RRC signaling according to a code rate, and anoffset value. Here, a PDCCH that releases SPS is called an SPS releasePDCCH, and a DL SPS release PDCCH that releases DL SPS transmissionrequires the transmission of an ACK/NACK signal.

Here, in the subframe n, UE sends ACK/NACK using the PUCCH formats 1a/1baccording to a PUCCH resource n^((1,p)) _(PUCCH). In n^((1,p)) _(PUCCH),p indicates an antenna port p. The k is determined by Table 5.

The PUCCH resource n^((1,p)) _(PUCCH) can be allocated as in thefollowing equation. P can be p0 or p1.n ^((1,p=p0)) _(PUCCH)=(M−m−1)·N _(c) +m·N _(c+1) +n _(CCE) +N ⁽¹⁾_(PUCCH) for antenna port p=p0,n ^((1,p=p1)) _(PUCCH)=(M−m−1)·N _(c) +m·N _(c+1)+(n _(CCE)+1)+N ⁽¹⁾_(PUCCH) for antenna port p=p1,  [Equation 3]

In Equation 3, c is selected in such a way as to satisfyN_(c)≦n_(CCE)<N_(c+1) (antenna port p0), N_(c)≦(n_(CCE)+1)<N_(c+1)(antenna port p1) from among {0, 1, 2, 3}. N⁽¹⁾ _(PUCCH) is a value setby a higher layer signal. N_(C)=max {0, floor [N^(DL) _(RB)·(N^(RB)_(sc)·c−4)/36]}. The N^(DL) _(RB) is a DL bandwidth, and N^(RD) _(sc) isthe size of an RB indicated by the number of subcarriers in thefrequency domain. n_(CCE) is a first CCE number used to send acorresponding PDCCH in a subframe n−k_(m). m is a value that makes k_(m)the smallest value in the set K of Table 5.

2) If UE detects an SPS PDSCH, that is, a PDSCH not including acorresponding PDCCH, in the DL subframe n−k of a primary cell, the UEcan send ACK/NACK in the subframe n using the PUCCH resource n^((1,p))_(PUCCH) as follows.

Since an SPS PDSCH does not include a scheduling PDCCH, UE sendsACK/NACK through the PUCCH formats 1a/1b according to n^((1,p)) _(PUCCH)that is configured by a higher layer signal. For example, 4 resources (afirst PUCCH resource, a second PUCCH resource, a third PUCCH resource,and a fourth PUCCH resource) can be reserved through an RRC signal, andone resource can be indicated through the Transmission Power Control(TPC) field of a PDCCH that activates SPS scheduling.

The following table is an example in which resources for channelselection are indicated by a TPC field value.

TABLE 7 TPC field value Resources for channel selection ‘00’ First PUCCHresource ‘01’ Second PUCCH resource ‘10’ Third PUCCH resource ‘11’Fourth PUCCH resource

For another example, it is assumed that in TDD, one serving cell isconfigured (i.e., only a primary cell is configured) in UE, ACK/NACKmultiplexing is used, and M>1. That is, it is assumed that a pluralityof DL subframes is associated with one UL subframe.

1) A PUCCH resource n⁽¹⁾ _(PUCCH,i) for sending ACK/NACK when UEreceives a PDSCH in a subframe n−k_(i) (0≦i≦M−1) or detects a DL SPSrelease PDCCH can be allocated as in the following equation. Here,k_(i)εK, and the set K has been described with reference to Table 5.n ⁽¹⁾ _(PUCCH,i)=(M−i−1)·N _(c) +i·N _(c+1) +n _(CCE,i) +N ⁽¹⁾_(PUCCH)  [Equation 4]

Here, c is selected from {0, 1, 2, 3} so that N_(c)≦n_(CCE,i)<N_(c+1) issatisfied. N⁽¹⁾ _(PUCCH) is a value set by a higher layer signal.N_(C)=max{0, floor [N^(DL) _(RB)·(N^(DL) _(sc)·c−4)/36]}. The N^(DL)_(RB) is a DL bandwidth, and N^(RB) _(sc) is the size of an RB indicatedby the number of subcarriers in the frequency domain. n_(CCE,i) is afirst CCE number used to send a corresponding PDCCH in the subframen−k_(i).

2) If UE receives a PDSCH (i.e., SPS PDSCH) not having a correspondingPDCCH in the subframe, n⁽¹⁾ _(PUCCH,i) is determined by a configurationgiven by a higher layer signal and Table 7.

If two or more serving cells have been configured in UE in TDD, the UEsends ACK/NACK using channel selection that uses the PUCCH format 1b orthe PUCCH format 3.

For example, if a plurality of serving cells using channel selectionthat uses the PUCCH format 1b has been configured, when ACK/NACK bitsare greater than 4 bits, UE performs spatial ACK/NACK bundling on aplurality of codewords within one DL subframe and sends spatiallybundled ACK/NACK bits for each serving cell through channel selectionthat uses the PUCCH format 1b. Spatial ACK/NACK bundling means thecompression of ACK/NACK for each codeword through logical AND operationswithin the same DL subframe.

If ACK/NACK bits are 4 bits or lower, spatial ACK/NACK bundling is notused and the ACK/NACK bits are transmitted through channel selectionthat uses the PUCCH format 1b.

For another example, if 2 or more serving cells using the PUCCH format 3have been configured in UE, when ACK/NACK bits are greater than 20 bits,spatial ACK/NACK bundling can be performed in each serving cell andACK/NACK bits subjected to spatial ACK/NACK bundling can be transmittedthrough the PUCCH format 3.

In the prior art, a precondition was that a plurality of serving cellsconfigured in UE has the same UL-DL configuration. In thenext-generation wireless communication system, however, each servingcell may have a different UL-DL configuration. In this case, some of thesame subframes for a plurality of serving cells may be configured to beDL subframes, and the remaining subframes may be configured to be ULsubframes.

Table 8 below shows that ACK/NACK is transmitted in what a subframeaccording to an UL-DL configuration when one serving cell operates inTDD.

TABLE 8 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 4  6 — 4 6— 1 7  6 4 7 6 4 2 7  6 4 8 7 6 4 8 3 4 11 7 6 6 5 5 4 12  11 8 7 7 6 54 5 12  11 9 8 7 6 5 4 13  6 7  7 7 7 5

When UE receives a PDSCH or a PDCCH (e.g., DL SPS release PDCCH)necessary for an ACK/NACK response in a subframe n, the UE sendsACK/NACK in a subframe ‘n+k(n)’. Each of the values of Table 8 indicatesthe k(n) value. For example, Table 8 indicates that if an UL-DLconfiguration is 0 and a PDSCH is received in a subframe 0, ACK/NACK istransmitted in a subframe 4 after four subframes. A specific time isnecessary in order for UE to send ACK/NACK after receiving a PDSCH or aDL SPS release PDCCH. A minimum value of this specific time ishereinafter indicated as ‘k_(min)’, and a value of k_(min) can be foursubframes. In Table 8, a point of time at which ACK/NACK is transmittedis described below. It can be seen that ACK/NACK is chiefly transmittedin the first UL subframe after ‘k_(min)’ elapses. However, an underlinenumber in Table 8 does not indicates the first UL subframe after‘k_(min)’ elapses, but indicates an UL subframe placed next. This is forpreventing ACK/NACK for too many DL subframes from being transmitted inone UL subframe.

[HARQ]

In UL, a BS schedules one or more resource blocks for selected UE inaccordance with a predetermined scheduling rule, and the UE sends datausing the allocated resources. An error control method when a frame islost or damaged after scheduling is performed and data is transmittedincludes an automatic repeat request (ARQ) method and a Hybrid ARQ(HARQ) method that is a more advanced form. Basically, in the ARQmethod, the transmission side waits for the coming of an acknowledgementmessage (ACK) after sending one frame. The reception side sends theacknowledgement message (ACK) only when the frame is normally received.If an error occurs in the frame, the reception side sends a negative-ACKor not-acknowledgement (NACK) message. Information about the erroneousframe is deleted from the buffer of the reception side. The transmissionside sends a subsequent frame when an ACK signal is received from thereception side, but retransmits the frame when a NACK message isreceived from the reception side.

Unlike in the ARQ method, in the HARQ method, if a received frame cannotbe demodulated, the reception side sends a NACK message to thetransmission side, but stores an already received frame in its bufferfor a specific time so that the already received frame is associatedwith a previously received frame when the already received frame isretransmitted in order to increase a reception success ratio. An HARQmethod more efficient than the basic ARQ method is recently used morewidely. The HARQ method includes various types. The HARQ method can bebasically divided into a synchronous HARQ and an asynchronous HARQdepending on retransmission timing and can be divided into achannel-adaptive method and a channel-non-adaptive method depending onwhether or not a channel state is incorporated into the amount ofresources that are used upon retransmission.

The synchronous HARQ method is a method of performing subsequent dataretransmission at timing determined by a system when the initialtransmission of data fails. For example, assuming that timing at whichdata retransmission is performed is performed every fourth timing(subframe) after an initial transmission fail signal is received, it isnot necessary to inform retransmission timing additionally because thetiming has already been agreed between a BS and UE. If the datatransmission side has received a NACK message, the data transmissionside retransmits data in a subframe at the next agreed timing. Thisprocess is repeated until an ACK message instead of a NACK message isreceived. For example, it has been agreed that data will beretransmitted in a fourth subframe after every NACK is received. Even inthe synchronous HARQ method, in order to control frequency resourceallocation for retransmission, a modulation scheme, etc., a controlchannel including scheduling information for the frequency resourceallocation, the modulation scheme, etc., can be transmitted.

In contrast, in the asynchronous HARQ method, even if there is anACK/NACK response, retransmission is not immediately performed inresponse to the ACK/NACK response, but retransmission timing is newlyscheduled or additional signaling can be performed. Timing at whichretransmission for previously failed data transmission is performed mayvary depending on various factors, such as a channel state.

The channel-non-adaptive HARQ method is a method in which a modulationscheme for data upon retransmission, the number of resource blocks used,and the like are performed as scheduled upon initial transmission. Incontrast, the channel-adaptive HARQ method is a method in which amodulation scheme for data, the number of resource blocks, and the likeare varied depending on the state of a channel. For example, in thechannel-non-adaptive HARQ method, the transmission side sends data using6 resource blocks upon initial transmission and likewise retransmitsdata using the 6 resource blocks upon retransmission. In contrast, inthe channel-adaptive HARQ method, although transmission was initiallyperformed using 6 resource blocks, retransmission is performed usingresource blocks larger than or smaller than the 6 resource blocksdepending on a channel state.

Four combinations of HARQ can be performed according to theclassification. HARQ methods that are chiefly used include anasynchronous and channel-adaptive HARQ method and a synchronous andchannel-non-adaptive HARQ method. The asynchronous and channel-adaptiveHARQ method can maximize retransmission efficiency by adaptively varyingretransmission timing and the amount of resources used depending on thestate of a channel, but this method is not commonly taken intoconsideration for UL because it has a disadvantage in that overhead isincreased. Meanwhile, the synchronous and channel-non-adaptive HARQmethod is advantageous in that there is almost no signaling overhead fortiming for retransmission and resource allocation because the timing forretransmission and the resource allocation are agreed within a system,but is disadvantageous in that retransmission efficiency is low if thismethod is used in a channel state that varies severely.

In current 3GPP LTE, an asynchronous HARQ method is used in downlink,and a synchronous HARQ method is used in uplink.

FIG. 9 shows an example of a DL HARQ.

Referring to FIG. 9, after scheduling information and data aretransmitted, information about ACK/NACK is received from UE and nextdata is transmitted. The next data can be new data or the retransmissiondata. As shown in FIG. 9, there is time delay until the next data istransmitted. Such time delay is caused by channel propagation delay anddelay generated due to the time taken for data decoding and dataencoding. A method of transmitting data using an independent HARQprocess for data transmission not having a blank during such a delayinterval is being used. For example, if the shortest period between datatransmission and the next data transmission is 7 subframes, 7independent HARQ processes can be placed so that data is transmittedwithout a blank. In LTE, if an operation is not performed according toMIMO, a maximum of 8 HARQ processes can be allocated.

An UL HARQ process includes a process of transmitting a scheduled PUSCHin response to an UL grant, receiving ACK/NACK for the PUSCH through aPHICH, and retransmitting the PUSCH if NACK is included in the PHICH.

Hereinafter, for convenience of description, a subframe interval until aPUSCH is transmitted after an UL grant is received is called k, and asubframe interval until a PHICH is received after the PUSCH istransmitted is called j. Furthermore, a subframe interval until thePUSCH is retransmitted after the PHICH is transmitted is called r, and asubframe interval until the PUSCH is retransmitted after an UL grant isreceived is called k′. k, j, r, and k′ are called an HARQ timingrelationship because timing at which an HARQ is performed can be awarebased on k, j, r, and k′.

FIG. 10 shows a synchronization HARQ process in FDD.

Referring to FIG. 10, assuming that a subframe that uses a PUSCH is asubframe n, a PDCCH is received in a subframe n−k. A PHICH is receivedin a subframe n+j, and a PUSCH is retransmitted in a subframe n+j+r. Inthis case, an UL grant for the retransmitted PUSCH is received in asubframe n+j+r−k′. That is, j+r is an interval during which a PUSCH forthe same HARQ process is retransmitted.

In FDD, each timing relationship in FIG. 10 remains constant because aratio of an UL subframe and a DL subframe is 1:1 and the UL subframe andthe DL subframe are contiguous. That is, k=j=r=k′=k_(min). k_(min) canbe 4 subframes. Accordingly, 8 UL subframes are present until UEretransmits a PUSCH after transmitting the PUSCH, and 8 different HARQprocesses can be performed.

In contrast, in TDD, a ratio of an UL subframe and a DL subframe may notbe 1:1. Assuming that k_(min)=4, k, j, r, and k′ values can vary.Furthermore, the values may not be constant. For example, the k, j, r,and k′ values can be changed depending on an UL-DL configuration of aTDD frame and a subframe number.

FIGS. 11 to 17 show examples of k, j, r, and k′ values according to theUL-DL configurations (refer to Table 1) of the TDD frame and subframenumbers. In FIGS. 11 to 17, numbers within subframes denote respectiveUL HARQ process numbers (hereinafter abbreviated as HARQ processnumbers), and numbers drawn in arrows denote respective subframeintervals. Here, an arrow drawn over the TDD frame indicates 1) that aPUSCH scheduled in response to an UL grant is transmitted in an ULsubframe after how many subframes from a DL subframe in which the ULgrant is received (k), or indicates that 2) a PUSCH is transmitted in anUL subframe after how many subframes from a subframe in which a PHICH isreceived (r), indicate that 3) a PUSCH is scheduled in response to an ULgrant and retransmitted in an UL subframe after how many subframe from aDL subframe in which the UL grant is received (k′). Furthermore, anarrow indicated under the TDD frame indicates that 4) a PHICH thatcarries ACK/NACK for a PUSCH in an UL subframe in which the PUSCH istransmitted is received in a DL subframe after how many subframe (j).

The subframes in which the HARQ process numbers are written are ULsubframes. The remaining subframes are DL subframes.

From FIG. 11, it can be seen that j+r=11 or j+r=13. From FIGS. 12 to 16,it can be seen that j+r=10, and from FIG. 17, it can be seen that avalue of j+r is 11, 13, or 14.

The HARQ timing relationships shown in FIGS. 11 to 17 are HARQ timingrelationships when UE accesses a single cell. In this case, a singlecell complies with a cell-specific UL-DL configuration. Thecell-specific UL-DL configuration can be broadcasted as the systeminformation (e.g., SIB-1) of the corresponding cell. The cell-specificUL-DL configuration is used when UE accesses a cell through a singlecarrier or initially accesses a primary cell to be described later.

In drawings following FIGS. 11 to 17, an HARQ process number and adescription generally given as an HARQ process number are for describingperiodicity in which the same HARQ process is used and the number ofHARQ processes, but there is no problem in that the present inventionare applied to the HARQ process number and the description although anactually fixed HARQ process number is not present. Furthermore,illustrated HARQ timing is only an embodiment for a description.

A carrier aggregation system is described below. The carrier aggregationsystem is also called a multiple carrier system.

A 3GPP LTE system supports the case where a DL bandwidth and an ULbandwidth are differently configured, but one Component Carrier (CC) isa precondition in this case. The 3GPP LTE system supports a maximum of20 MHz and supports only one CC in each of UL and DL although an ULbandwidth may be different from a DL bandwidth.

A carrier aggregation (or a bandwidth aggregation) (also called aspectrum aggregation) supports a plurality of CCs. For example, if 5 CCsare allocated as a granularity of each carrier having a 20 MHzbandwidth, a bandwidth having a maximum of 100 MHz can be supported.

One DL CC or a pair of an UL CC and a DL CC can correspond to one cell.Accordingly, UE that communicates with a BS through a plurality of DLCCs can be said to be served from a plurality of serving cells.

FIG. 18 is a comparison example of a single carrier system and a carrieraggregation system.

A carrier aggregation system (FIG. 18( b)) includes three DL CCs andthree UL CCs, but the number of each of DL CCs and UL CCs is notlimited. A PDCCH and a PDSCH can be independently transmitted inrespective DL CCs, and a PUCCH and a PUSCH can be independentlytransmitted in respective UL CCs. Alternatively, a PUCCH may betransmitted only through a specific UL CC.

Since three pairs of a DL CC and an UL CC are defined, UE can be said tobe served from three serving cells.

The UE can monitor a PDCCH in a plurality of DL CCs and receive DLtransport blocks through the plurality of DL CCs at the same time. TheUE can send a plurality of UL transport blocks through a plurality of ULCCs at the same time.

A pair of a DL CC #A and an UL CC #A can become a first serving cell, apair of a DL CC #B and an UL CC #B can become a second serving cell, anda pair of a DL CC #C and an UL CC#C can become a third serving cell.Each of the serving cells can be identified by a Cell index (CI). The CIcan be unique within a cell or may be UE-specific.

A serving cell can be divided into a primary cell and a secondary cell.The primary cell is a cell on which UE performs an initial connectionestablishment procedure or initiates a connection re-establishmentprocedure or a cell designated as a primary cell in a handover process.The primary cell is also called a reference cell. The secondary cell canbe configured after an RRC connection has been established and can beused to provide additional radio resources. At least one primary cell isalways configured, and a secondary cell can be added/modified/releasedin response to higher layer signaling (e.g., an RRC message). The CI ofa primary cell can be fixed. For example, the lowest CI can bedesignated as the CI of a primary cell.

Such a carrier aggregation system can support cross-carrier scheduling.Cross-carrier scheduling is a scheduling method capable of allocatingPDSCH resources, transmitted through another CC, through a PDCCHtransmitted through a specific CC and/or of allocating PUSCH resourcestransmitted through CCs other than a CC basically linked to the specificCC. That is, a PDCCH and a PDSCH can be transmitted different DL CCs,and a PUSCH can be transmitted through an UL CC different from an UL CCthat is basically linked to a DL CC through which a PDCCH including anUL grant is transmitted. As described above, in a system that supportscross-carrier scheduling, there is a need for a carrier indicator thatinforms, through a PDCCH, that a PDSCH/PUSCH providing controlinformation is transmitted through what DL CC/UL CC. A field includingsuch a carrier indicator is called a Carrier Indication Field (CIF).Hereinafter, a scheduling carrier or a scheduling cell means a carrieror a serving cell through which an UL grant or a DL grant istransmitted, and a scheduled carrier or a scheduled cell means a carrieror a serving cell through which a data channel is received ortransmitted in response to the UL grant or the DL grant.

Non-cross-carrier scheduling is a scheduling method extended from anexisting scheduling method. That is, non-cross-carrier scheduling is ascheduling method of transmitting a PDSCH and a PDCCH for scheduling thePDSCH within the same DL CC. Furthermore, non-cross-carrier schedulingis a scheduling method of transmitting a PDCCH for scheduling a PUSCH ina DL CC and transmitting a PUSCH in an UL CC that is basically linked tothe DL CC.

In an existing carrier aggregation system, it was a precondition thatserving cells use only radio frames having the same type. Furthermore,it was a precondition that if each serving cell operates according toTDD, a TDD frame is used, but the serving cells have the same UL-DLconfiguration. In the next-generation carrier aggregation system,however, the case where each serving cell uses a different UL-DLconfiguration is also taken into consideration.

FIG. 19 shows an example in which each serving cell uses a differentUL-DL configuration. If serving cells use different UL-DL configurationsas described above, some subframes can become valid or invalidsubframes. Here, the valid subframe means a DL or UL subframe in whichdata can be actually transmitted, and the invalid subframe means a DL orUL subframe in which data cannot be transmitted. In order for a subframeto become a valid subframe, a data channel itself needs to betransmitted in the corresponding subframe, and a control channel alsoneeds to be transmitted in the corresponding subframe in a time interval(subframe) defined such that the control channel corresponding to thedata channel (i.e., generating the transmission of the data channel) istransmitted. The following description is an example of a method ofconfiguring valid and invalid subframes.

Referring to FIG. 19, a first serving cell and a second serving cellthat are used in a TDD frame can be allocated. Here, the first servingcell and the second serving cell can use different UL-DL configurations.For example, a subframe #N of the first serving cell can be set as U,and a subframe #N of the second serving cell can be set as D. In thiscase, UE operating in half duplex can selectively use only one of UL andDL transmission directions in relation to the two serving cells, and thesubframe #N having a transmission direction different from that selectedin another serving cell can become an invalid subframe 801. For example,assuming that the transmission direction of the UE is set as an ULdirection in the subframe #N and the subframe #N of the first servingcell is an UL subframe, the subframe #N of the first serving cell can beused as a valid subframe. In contrast, if the subframe #N of the secondserving cell is a DL subframe, the subframe #N of the second servingcell becomes an invalid subframe. The UE operating in half duplex maynot use an invalid subframe. The state of an invalid subframe that isnot used as described above can be indicated by X in order todistinguish the invalid subframe from existing D, U, and S. Allsubframes set as D or U in the first serving cell and the second servingcell may be valid subframes. Furthermore, a special subframe S is asubframe that includes a gap (e.g., a Guard Period (GP)). The specialsubframe can become a DL valid subframe or a DL invalid subframedepending on configurations, such as a gap size.

The present invention can be applied to the case where cross-carrierscheduling is used in a carrier aggregation system in which a pluralityof serving cells is aggregated. Here, it is a precondition that theserving cells can use different UL-DL configurations. One of the UL-DLconfigurations applied to the serving cells can be used as a referenceUL-DL configuration. For example, an UL-DL configuration applied to aprimary cell can be used as a reference UL-DL configuration.

Here, in the case of a subframe in which a transmission direction (UL orDL) according to a cell-specific UL-DL configuration for a specificserving cell is not identical with a transmission direction according tothe reference UL-DL configuration, UE can designate the correspondingsubframe as ‘X’ in which the corresponding subframe is not used.

In the case of UE that operates in full duplex in a carrier aggregationbetween cells in which different UL-DL configurations are used, areference UL-DL configuration for uplink HARQ timing can be determinedas follows.

For example, if UL subframes in the cell-specific UL-DL configuration ofa secondary cell are a subset of UL subframes defined in thecell-specific UL-DL configuration of a primary cell, the reference UL-DLconfiguration of the secondary cell can become the UL-DL configurationof the primary cell. In this case, an UL subframe of the secondary cellthat does not form an intersection with a valid UL subframe of theprimary cell can become an invalid subframe.

For another example including the above example, an UL-DL configurationin which all DL subframes are included in a DL subframe intersectionformed by the cell-specific UL-DL configuration of a secondary cell andby the cell-specific UL-DL configuration of a primary cell (i.e., a setof subframes that are DL subframes in the two serving cells) can becomethe reference UL-DL configuration of the secondary cell. Preferably, anUL-DL configuration in which the number of DL subframes is the largestas compared with UL subframes can be selected. In this case, subframesof the secondary cell that do not form an UL subframe intersection withthe reference UL-DL configuration (i.e., a set of all subframesconfigured to be UL subframes in the cell-specific UL-DL configurationand the reference UL-DL configuration) can become invalid subframes.

In the case of UE that operates in half duplex in a carrier aggregationbetween cells in which different UL-DL configurations are used, areference UL-DL configuration for uplink HARQ timing can be determinedas follows.

For example, if UL subframes in the cell-specific UL-DL configuration ofa secondary cell are a subset of UL subframes defined in thecell-specific UL-DL configuration of a primary cell, the reference UL-DLconfiguration of the secondary cell can become the UL-DL configurationof the primary cell. In this case, an UL subframe of the secondary cellthat does not form an intersection with a valid UL subframe of theprimary cell becomes an invalid subframe. Here, the UL subframe does notbecome an X subframe.

For another example including the above examples, like in the case offull duplex, an UL-DL configuration in which all DL subframes areincluded in the DL subframe intersection of the cell-specific UL-DLconfiguration of a secondary cell and the cell-specific UL-DLconfiguration of a primary cell can be used as the reference UL-DLconfiguration of the secondary cell. Preferably, an UL-DL configurationin which the number of DL subframes is the greatest than the number ofUL subframes can be selected. In this case, an UL subframe of thesecondary cell that does not form an UL subframe intersection with thereference UL-DL configuration becomes an invalid subframe. Furthermore,if an X subframe is generated because cells aggregated with acell-specific UL-DL configuration have different transmissiondirections, the X subframe can become an invalid subframe.

FIG. 20 shows a problem in a process of performing a synchronous HARQwhen each serving cell uses a different UL-DL configuration.

Referring to FIG. 20, a primary cell uses an UL-DL configuration 0, anda secondary cell uses an UL-DL configuration 1. Hereinafter, kc, jc, rc,kc′, jc′, and rc′ indicate an HARQ timing relationship between a DLsubframe of the primary cell and an UL subframe of the secondary cellwhen cross-carrier scheduling is used.

kc and jc can be configured to make the fastest response which satisfiesk_(min). If different UL-DL configurations are used, control informationcapable of distinguishing UL subframes needs to be included in an ULgrant because one UL grant can schedule a plurality of UL subframes.Furthermore, from FIG. 20, it can be seen that HARQ process numbers ofsome HARQ processes are changed. In order to solve this problem, thefollowing method can be used.

An HARQ process of a serving cell (a secondary cell, indicated by SCC)that is subject to cross-carrier scheduling can switch to anasynchronous HARQ process not to a synchronous HARQ process. To thisend, information that informs an HARQ process number can be included ina DCI format for scheduling the secondary cell. The HARQ process numbermay be known by using some fields of the DCI format and may be known byadding a new field.

If the length of a DCI format for scheduling a primary cell is differentfrom that of a DCI format for scheduling a secondary cell, blinddecoding overhead for UE can be increased. Accordingly, it is preferredthat the lengths of the two DCI formats be made the same. To this end,if a field indicative of an HARQ process number is added to the DCIformat for scheduling the secondary cell, a field indicative of an HARQprocess number can be added to the DCI format for scheduling the primarycell. The field indicative of the HARQ process number that is added tothe DCI format for scheduling the primary cell can be used for anasynchronous HARQ process in the primary cell. Alternatively, thesynchronous HARQ process is maintained in the primary cell, but thefield indicative of the HARQ process number can be used for otherpurposes.

The method is not necessarily used upon cross-carrier scheduling and maybe applied to the case where an UL subframe of each serving cell and ascheduling criterion for a DL subframe are changed uponnon-cross-carrier scheduling.

FIG. 21 shows a process of performing a synchronous HARQ when eachserving cell uses a different UL-DL configuration.

Referring to FIG. 21, UL grant transmission time points for different ULsubframes of a secondary cell are configured to not overlap with eachother, and the UL grant transmission time points are distributed so thatthe fastest response satisfying k_(min) can be performed.

A secondary cell SCC operates as j+r=10 in the case of non-cross-carrierscheduling and operates as jc+rc=15 in the case of cross-carrierscheduling. In this case, all the HARQ processes of the secondary cellhave different HARQ process numbers. In order to solve this problem, thenumber of HARQ processes can be increased.

That is, the number of HARQ processes of a secondary cell which aresubject to cross-carrier scheduling can be configured to be the same asthe number of UL subframes of the secondary cell (as illustrated in FIG.21, one UL subframe of a start point and a retransmission time point isexcluded from the number because a period is repeated) which are presentup to the initial PUSCH transmission time point of the secondary celland the PUSCH retransmission time point of a synchronous HARQ processfor an ACK/NACK response through a PHICH (i.e., between the regressionperiods of the same HARQ process). As shown in the example of FIG. 21,the number of HARQ processes is 4 when operating as a single cell or atthe time of non-cross-carrier scheduling. In the case of cross-carrierscheduling, however, since the regression period of the same HARQprocess is changed, the number of UL subframes (Here, an UL subframe inwhich a PUSCH is retransmitted is excluded from the number of ULsubframes) including the UL subframe of an initial PUSCH transmissiontime point up to a PUSCH retransmission time point becomes 6. As aresult, the number of HARQ processes becomes 6. Here, the number of ULsubframes can be limited to the number of valid UL subframes. That is,although a subframe is configured to be an UL subframe according to acell-specific UL-DL configuration, UE cannot use the UL subframe if thetransmission of a control channel (PDCCH) for scheduling the datachannel (PUSCH) of the UL subframe is not defined in a scheduling cell.Furthermore, if some subframes are configured to be DL subframesaccording to the UL-DL configuration of each serving cell, UE operatingin half duplex cannot use the corresponding subframes. Accordingly, thenumber of HARQ processes can be configured to be the same as the numberof valid UL subframes not including the invalid UL subframes. The numberof HARQ processes determined by taking cross-carrier scheduling intoconsideration as described above can also be applied to the number ofHARQ processes upon non-cross-carrier scheduling for the simplicity of aUE implementation.

As another method, in the case of a carrier aggregation between cells inwhich different UL-DL configurations are used or a carrier aggregationusing different duplex methods (i.e., an aggregation of a carrier usingFDD and a carrier using TDD), an agreed value can be used as the numberof HARQ processes, or a BS can determine the number of HARQ processesand inform UE of the number of HARQ processes through signaling. Thesignaling can be performed through an RRC message. This can be appliedto only the number of HARQ processes of a secondary cell which aresubject to cross-carrier scheduling. Here, a cell subject tonon-cross-carrier scheduling uses the number of HARQ processes that isdefined in a corresponding UL-DL configuration of a corresponding duplexmethod. This method can be used to determine the number of downlink HARQprocesses as well as the number of uplink HARQ processes.

FIG. 22 shows a process of performing a synchronous HARQ when eachserving cell uses a different UL-DL configuration.

The UL grant of a scheduling cell and UL data transmission timing of ascheduled cell are configured upon cross-carrier scheduling (S310). Thescheduling cell can be a primary cell, and the scheduled cell can be asecondary cell.

A BS increases the HARQ process period of the scheduled cell by a wholenumber times the HARQ period in the case where one serving cell isallocated to UE (S320). Here, the HARQ process period means a subframeinterval between a subframe in which UL data is transmitted and asubframe right before a subframe in which the UL data is retransmittedor new UL data is transmitted. The HARQ process period is also called anHARQ period and may also be called an HARQ regression period.

The BS performs an HARQ at the increased HARQ process period along withthe UE (S330).

FIG. 23 shows HARQ timing when the method of FIG. 22 is used.

Referring to FIG. 23, an UL-DL configuration 0 is used in a primarycell, and an UL-DL configuration 1 is used in a secondary cell. UEreceives an UL grant for an UL subframe of the secondary cell throughthe primary cell (grant(n−kc)) and sends UL data in the UL subframe ofthe secondary cell based on the UL grant (PUSCH(n)). If anacknowledgment/not-acknowledgement (ACK/NACK) signal for the UL data isreceived through a PHICH through the primary cell (PHICH(n+jc)) and theACK/NACK signal is NACK, the UE sends retransmission data for the ULdata in the UL subframe of the secondary cell (PUSCH retx(n+jc+rc)).Here, an interval between the UL data transmission and the UL dataretransmission, that is, the HARQ period, is a whole number times theHARQ period in the case where one serving cell is allocated to the UE.That is, if non-cross-carrier scheduling is used in the secondary cell,j+r=10. In contrast, if cross-carrier scheduling is used in thesecondary cell, jc+rc=20. That is, the HARQ process period of thesecondary cell is doubled.

If cross-carrier scheduling is used, PHICH response timing can beconfigured (jc) with minimum delay as indicated by a dotted line in FIG.23, and an rc value is set in PUSCH retransmission therefor so that therc value is mapped to the same HARQ process as that applied in a singleserving cell.

Here, some UL subframes of the secondary cell can be skipped withoutbeing used in HARQ processes allocated to the corresponding ULsubframes. That is, some UL subframes of the secondary cell are not usedin non-adaptive-synchronous HARQ process retransmission that responds toa PHICH without an UL grant.

If an UL grant for an HARQ process number between PUSCH initialtransmission (indicated by PUSCH(n)) and PUSCH retransmission (indicatedby PUSCH retx (n+jc+rc)) that have the same HARQ process number (e.g.,0) is present, retransmission or new PUSCH transmission can be statedirrespective of the PHICH response.

Alternatively, a limit may be applied to an UL grant for an HARQ processnumber between the PUSCH initial transmission (indicated by PUSCH(n))and the PUSCH retransmission (indicated by PUSCH retx (n+jc+rc)) thathave the same HARQ process number (e.g., 0) so that the UL grant is nottransmitted. In this case, UE may not search for the UL grant oncondition that the limited UL grant is not transmitted.

In FIG. 23, if an HARQ process is to be allocated in skipped subframes,HARQ processes having the same number as the number of UL subframes of asecondary cell which are present between the initial PUSCH transmissiontime point of the secondary cell and the PUSCH retransmission time pointof a synchronous HARQ process for an ACK/NACK response through a PHICHcan be allocated. In this example, if HARQ processes operate as a singlecell, the number of HARQ processes is 4, but the number of HARQprocesses is doubled to become 8 in the case of cross-carrierscheduling. In this case, the number of UL subframes between the initialPUSCH transmission time point and the PUSCH retransmission time pointcan be limited to the number of valid UL subframes. If a retransmissionPUSCH is transmitted in n+jc+rc′, a BS can send an UL grant for theretransmission PUSCH in n+jc+rc−kc′.

Alternatively, if the retransmission PUSCH is transmitted in n+jc+rc,the BS can send the UL grant for the retransmission PUSCH in n+jc. Thatis, the BS can send the UL grant at the same time point as a time pointat which a PHICH for the initial PUSCH transmission is transmitted.

Alternatively, in cross-carrier scheduling, PUSCH retransmission may bemapped to the same HARQ process as that of the case where minimum delay(jc+rc) and a single serving cell are configured, and PHICH transmissiontiming n+jc′ may be configured to be the same as timing at which an ULgrant for the retransmission PUSCH is transmitted, that is, n+jc+rc−kc′,not as PHICH timing configured with minimum delay (i.e., jc). In thiscase, rc′=kc′.

FIGS. 24 and 25 show examples in which the number of HARQ processes ismade identical with an HARQ process period by equally distributing ULgrants and PHICH transmission time points.

That is, the examples of FIGS. 24 and 25 correspond to the case wherethe number of HARQ processes is identical with a period in the casewhere a single serving cell is configured and the case where a pluralityof serving cells is configured and cross-carrier scheduling is used.

To this end, if a single serving cell is configured, an aggregationbetween serving cells that include UL-DL configurations having the sameHARQ process period (j+r) can be allowed. That is, a carrier aggregationis allowed between serving cells having UL-DL configurations 1, 2, 3, 4,and 5 wherein j+r=10.

Furthermore, an UL grant for a PUSCH can be transmitted at the sametiming irrespective of whether the PUSCH is initially transmitted orretransmitted. Here, PHICH transmission timing on which whether or notthe PUSCH corresponds to non-adaptive-synchronous HARQ retransmissioncan be made identical with the timing of the UL grant.

FIG. 26 shows a problem that may occur when serving cells in which anUL-DL configuration having the same j+r value is used are aggregated.

From FIG. 26, it can be seen that a PUSCH is retransmitted with aperiodic interval of 10 subframes in the HARQ processes 0, 1, and 2 of asecondary cell. However, the retransmission period of the HARQ process 3is not the 10 subframes. Even when serving cells in which an UL-DLconfiguration having the same j+r value is used are aggregated, the HARQperiods of some HARQ processes may not be constant.

In order to solve this problem, the following methods can be used.

1) An UL subframe not matched with an HARQ period as in the HARQ process3 may be excluded from PUSCH transmission.

2) If a subframe is not matched with an HARQ period as in the HARQprocess 3, the subframe can be retransmitted in a next period. That is,this method is a method of increasing an HARQ period. UL subframes thatare halfway skipped due to the increased HARQ period can be allocated toanother HARQ process. The number of additionally allocated HARQprocesses is dependent on the increased HARQ period. That is, when anHARQ period is increased N times, the number of additionally allocatedHARQ processes becomes N−1. For example, in FIG. 26, if the HARQ periodof the HARQ process 3 is doubled, an HARQ process 4 can be allocated toone UL subframe that is halfway skipped. In this case, the HARQprocesses 0, 1, and 2 and the HARQ process 3 have different HARQperiods.

In UL subframes to which an HARQ process is added, the number of addedHARQ processes and/or an HARQ process period may be differentlyconfigured every UL subframe or UL subframe group, and an agreed valueor a value signaled through RRC can be used as the number of added HARQprocesses and/or an HARQ process period.

3) Method of changing the number of HARQ processes.

FIG. 27 shows a method of changing the number of HARQ processes.

Referring to FIG. 27, in this method, in timing configured to have aresponse having minimum delay, the same HARQ process is configured in apair of UL subframes having a maximum jc+rc, and the number of HARQprocesses is determined depending on the number of UL subframes that arepresent between the same HARQ processes.

In the case of a secondary cell, the number of HARQ processes is 4 if asingle serving cell is configured, but is 5 as in FIG. 27 if a pluralityof serving cells is configured.

An agreed value can be used as the number of HARQ processes that aresubject to cross-carrier scheduling, or a BS can determine the number ofHARQ processes and inform UE of the number of HARQ processes throughsignaling using an RRC message.

4) Method of excluding PUSCH transmission having UL grant timing for aretransmission PUSCH, which is not identical with PHICH transmissiontiming.

FIG. 28 shows the method 4).

Referring to FIG. 28, in PHICH timing and retransmission UL granttiming, the HARQ processes 0 and 1 of a secondary cell have the sametiming, but the HARQ processes 2 and 3 thereof do not have the sametiming. In this case, PUSCH transmission in UL subframe in which theHARQ processes 2 and 3 are performed is excluded. That is, in FIG. 28,in the TDD frame of the secondary cell, third and fourth subframes areused in UL PUSCH transmission, and eighth and ninth subframes are notused.

5) Method of matching PHICH transmission timing with UL grant timing fora retransmitted PUSCH by shifting the frame boundaries of a primary celland a secondary cell.

FIG. 29 shows a method of performing an HARQ according to the method 5).

Referring to FIG. 29, the frame boundaries of a plurality of servingcells configured in UE can be shifted by the subframe without matchingthe frame boundaries with each other. A shifted value is a value onwhich the HARQ process periods of all the UL subframes of a secondarycell are maintained. Furthermore, PHICH transmission timing can bematched with UL grant transmission timing for a retransmission PUSCH. Anagreed and fixed value can be used as the shift value having thesubframe unit, or a BS can inform UE of the shift value throughsignaling using an RRC message.

Meanwhile, in an UL-DL configuration, DL-UL switch-point periodicity canbe 5 ms or 10 ms. In a similar channel environment, there is a goodpossibility that the same DL-UL switch-point periodicity may be used,and UL-DL configurations having the same switch-point periodicity have asimilar timing relationship. Furthermore, in the case of UE thatsupports half duplex, there is a problem in that an S subframe needs tobe added if serving cells having UL-DL configurations having DL-ULswitch-point periodicity with different periods are aggregated.

Accordingly, a method of allowing only a carrier aggregation betweenserving cells having UL-DL configurations having the same DL-ULswitch-point periodicity may be taken into consideration. That is, anaggregation may be allowed between serving cells having a 5 ms period,or an aggregation may be allowed only between serving cells having a 10ms period.

The above-described methods can be used in combination. Furthermore, themethods do not need to be necessarily used in a carrier aggregationsystem. For example, the above-described methods can be used when an ULgrant and PHICH transmission are configured only in a specific DLsubframe of one carrier (one TDD serving cell) and a timing relationshipwith a PUSCH in the same carrier is set up.

FIG. 30 shows an example in which the present invention is applied to asingle serving cell.

Referring to FIG. 30, the subframes of a primary cell include a DLsubframe (this is indicated by default DL), an UL subframe (this isindicated by default UL), and a flexible UL/DL subframe (this isindicated by flexible UL/DL). The DL subframe includes a PDCCH region.The flexible UL/DL subframe is a subframe which can be used as an ULsubframe or a DL subframe. If a plurality of serving cells isconfigured, the DL subframe of a primary cell can be replaced with aspecific DL subframe that is configured to enable UL grant and PHICHtransmission in a single cell.

Meanwhile, in a timing relationship between the PHICH of a primary celland the PUSCH of a secondary cell, PHICH resources may not be configuredin the primary cell. This is because there is a DL subframe not havingmapping between the PUSCH and the PHICH in a single carrier condition inwhich only the primary cell has been configured. In this case, asynchronous HARQ process operation can be performed as follows.

If PHICH resources are not present in the DL subframe of a PHICHtransmission carrier (this is called CC_h) corresponding to the ULsubframe of a carrier (this is called CC_s) through which a PUSCH istransmitted, PHICH transmission may not be performed.

Furthermore, a PUSCH retransmission UL subframe corresponding to PHICHtiming, a non-adaptive-synchronous HARQ process of performing anautomatic retransmission operation based on a response to the PHICHwithout an UL grant may not be allowed.

If a retransmission is needed in a corresponding HARQ process, anadaptive synchronous HARQ process, where a retransmission is performedby an UL grant, can be performed.

For example, UE has transmitted UL data in the first UL subframe of asecondary cell, but it may be difficult to allocate PHICH resources to aDL subframe of a corresponding primary cell. In this case, a BS does nottransmit ACK/NACK for the UL data through a PHICH. Instead, the BS cantransmit an UL grant for scheduling the second UL subframe of thesecondary cell. For a PUSCH to be retransmitted according to thecorresponding PHICH timing, the UL grant includes information indicatingwhether or not the UL data will be retransmitted. For example, anexisting New Data Indicator (NDI) bit can be used, or a new fieldindicating whether or not to perform retransmission can be added andtransmitted.

The reason why a DL subframe in which PHICH resources are not configuredis present in the DL subframes of a primary cell is that a DL subframenot having mapping between a PUSCH and a PHICH is present in a singlecarrier condition in which only a primary cell has been configured asdescribed above. The DL subframe not having the mapping includes DLsubframes indicated by D in the following table.

TABLE 9 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 1 D D 2 D DD D D D 3 D D D D 4 D D D D D D 5 D D D D D D D D 6

UE does not attempt to receive a PHICH in a subframe (subframe indicatedby D) in which a PHICH has not been configured. Regarding the PUSCH tobe retransmitted according to the PHICH timing of the subframe, UE candetermine whether or not to perform UL data retransmission based onwhether or not a New Data Indicator (NDI) bit included in an UL granthas been toggled (e.g., the UE determines that UL data retransmissionhas not been instructed if the NDI bit has been toggled and determinesthat UL data retransmission has been instructed if the NDI bit has notbeen toggled). If, as a result of the determination, it is determinedthat UL data retransmission has not been instructed, the UE has only tosend new data in a second UL subframe based on the UL grant. If, as aresult of the determination, it is determined that UL dataretransmission has been instructed, the UE has only to retransmit the ULdata in the second UL subframe. Here, the UE can adaptively retransmitthe UL data using a Modulation and Coding Scheme (MCS), transmissionpower, etc. which are different from those in initial UL transmission ina first UL subframe, based on the UL grant.

A method of stopping non-adaptive-synchronous HARQ retransmission asdescribed above can be used only when there is no PHICH in the DLsubframe of a PHICH transmission carrier CC_h that corresponds to thePUSCH transmission UL subframe of a PUSCH transmission carrier CC_s.

Alternatively, if there is no PHICH in any of the DL subframes of aPHICH transmission carrier CC_h corresponding to the PUSCH transmissionUL subframes of a PUSCH transmission carrier CC_s, the methods can beapplied to all the PUSCHs of the corresponding PUSCH transmissioncarrier CC_s.

Alternatively, the methods can be applied to all PUSCH transmissioncarriers CC_s irrespective of a DL subframe not having a PHICH.Exceptionally, the methods can be applied to only a secondary cellexcept a primary cell. Any one of the three methods can be used, or anyone of the three methods can be selected in response to an RRC message.

A PHICH transmission carrier CC_h is the same as a carrier in which aPDCCH for scheduling a PUSCH is transmitted, and a PUSCH transmissioncarrier CC_s is a carrier in which the PUSCH is transmitted. In the caseof cross-carrier scheduling, a PUSCH transmission carrier CC_s canbecome a secondary cell, and a PHICH transmission carrier CC_h canbecome a primary cell. In the case of non-cross-carrier scheduling, aPUSCH transmission carrier CC_s and a PHICH transmission carrier CC_hcan become the same carrier.

If a PUSCH transmission carrier CC_s and a PHICH transmission carrierCC_h are the same and PHICH resources are not present, new timinggenerated due to a carrier aggregation of different UL-DL configurationscan be used instead of PUSCH-PHICH timing that is defined in the UL-DLconfiguration of a corresponding carrier. The PHICH transmission carriercan be applied to only UE operating in half duplex.

FIG. 31 shows HARQ timing according to subframe bundling in FDD.

In FDD, subframe bundling refers to a scheme for increasing uplink cellcoverage by repeatedly sending a PUSCH during several subframes. Even inthis case, in order to guarantee k_(min)=4, configurations, such as thenumber of HARQ processes, UL grant timing, and PHICH timing, may bedifferent from those in the case where subframe bundling is not used.Accordingly, when an aggregation between carriers that use differentUL-DL configurations is performed, subframe bundling can be allowed onlyin a primary cell. Alternatively, subframe bundling can be allowed onlyin non-cross-carrier scheduling.

If a primary cell operates in FDD and a secondary cell operates in TDD,there is no timing restriction because UL transmission and DL receptionare possible in all the subframes of the primary cell. Accordingly, thesame HARQ timing as that of a single carrier configuration can be used.In this case, subframe bundling can be allowed even in the secondarycell.

All the above-described methods have been illustrated as being used oncondition that a plurality of serving cells is aggregated, each of theserving cells uses a different UL-DL configuration, and cross-carrierscheduling is used, but not limited thereto. That is, the methods can beapplied to the case where scheduling criteria for an UL subframe and aDL subframe are changed or the use of an UL subframe and a DL subframeis limited in a carrier using non-cross-carrier scheduling.

In accordance with the above-described methods, if a plurality ofserving cells is an aggregated, each of the serving cells uses adifferent UL-DL configuration, and cross-carrier scheduling is used,retransmission timing according to a synchronous HARQ process can beeffectively configured.

FIG. 32 is a block diagram showing a wireless apparatus in which anembodiment of the present invention is implemented.

A BS 100 includes a processor 110, memory 120, and a Radio Frequency(RF) unit 130. The processor 110 implements the proposed functions,processes and/or methods. For example, the processor 110 sends an ULgrant through a primary cell and receives UL data from UE through asecondary cell. Furthermore, the processor 110 sends ACK/NACK for the ULdata through the primary cell and receives retransmitted UL data throughthe secondary cell. In this case, an interval between a time point atwhich the UL data is received and a time point at which theretransmitted UL data is received can be called an HARQ period. HARQtiming for determining the HARQ period has been described above.Furthermore, the processor 110 can include information indicative ofwhether or not to retransmit the ACK/NACK for the received UL data inthe UL grant and send the UL grant, instead of sending the ACK/NACK forthe received UL data through a PHICH. The memory 120 is connected withthe processor 110, and it stores various pieces of information fordriving the processor 110. The RF unit 130 is connected with theprocessor 110, and it transmits and/or receives radio signals.

UE 200 includes a processor 210, memory 220, and an RF unit 230. Theprocessor 210 implements the proposed functions, processes and/ormethods. For example, the processor 210 receives the UL grant of asecondary cell through a primary cell and sends UL data in a secondarycell based on the UL grant. Next, the processor 210 receives anacknowledgment/not-acknowledgement (ACK/NACK) signal for the UL datathrough the primary cell. If the ACK/NACK signal is NACK, the processor210 sends retransmission data for the UL data in the secondary cell. Asdescribed above, a primary cell and a secondary cell use different UL-DLconfigurations. Furthermore, an HARQ period indicative of an intervalbetween an UL data transmission time point and an UL data retransmissiontime point can be a whole number times the HARQ period in the case whereone serving cell is allocated to UE. Furthermore, the processor 210 doesnot attempt to decode a PHICH in a specific DL subframe and determineswhether or not to retransmit the UL data based on information indicatingwhether or not to retransmit the UL data, which is included in an ULgrant. The specific DL subframe has been described above with referenceto Table 9. The memory 220 is connected with the processor 210, and itstores various pieces of information for driving the processor 210. TheRF unit 230 is connected with the processor 210, and it transmits and/orreceives radio signals.

The processor 110, 210 may include Application-Specific IntegratedCircuits (ASICs), other chipsets, logic circuits, data processors, andconverters for mutually converting baseband signals and radio signals.The memory 120, 220 may include Read-Only Memory (ROM), Random AccessMemory (RAM), flash memory, memory cards, storage media and/or otherstorage devices. The RF unit 130, 230 may include one or more antennasfor transmitting and/or receiving radio signals. When an embodiment isimplemented in software, the above-described scheme may be implementedas a module (process or function) that performs the above function. Themodule may be stored in the memory 120, 220 and executed by theprocessor 110, 210. The memory 120, 220 may be placed inside or outsidethe processor 110, 210 and may be connected to the processor 110, 210using a variety of well-known means

Although some embodiments of the present invention have been describedabove, a person having ordinary skill in the art will appreciate thatthe present invention may be modified and changed in various wayswithout departing from the technical spirit and scope of the presentinvention. Accordingly, the present invention is not limited to theembodiments and it may be said that the present invention includes allembodiments within the scope of the claims below.

What is claimed is:
 1. A method of performing, by a user equipment towhich a plurality of serving cells based on Time Division Duplex (TDD)has been allocated, a hybrid automatic repeat request (HARQ), the methodcomprising: receiving an uplink (UL) grant for a first subframe of asecond serving cell through a first serving cell; transmitting UL datain the first subframe of the second serving cell based on the UL grant;and performing a non-adaptive retransmission for the UL data in a secondsubframe of the second serving cell if a not-acknowledgement (NACK) forthe UL data is received through a physical HARQ indicator channel(PHICH) in a subframe i of the first serving cell, wherein the firstserving cell and the second serving cell use different uplink-downlink(UL-DL) configurations, and each of the UL-DL configurations isinformation on which each subframe within a TDD frame is configured asan UL subframe, a DL subframe or a special subframe, and wherein if aPHICH resource corresponding to the UL data is not present in thesubframe i, the non-adaptive retransmission is not allowed in the secondsubframe of the second serving cell.
 2. A method of performing, by auser equipment to which a plurality of serving cells based on TimeDivision Duplex (TDD) has been allocated, a hybrid automatic repeatrequest (HARD), the method comprising: receiving an uplink (UL) grantfor a first subframe of a second serving cell through a first servingcell; transmitting first UL data in the first subframe of the secondserving cell based on the UL grant; and performing a non-adaptiveretransmission for the first UL data in a second subframe of the secondserving cell if a not-acknowledgement (NACK) for the first UL data isreceived through a physical HARQ indicator channel (PHICH) in a subframei of the first serving cell, wherein the first serving cell and thesecond serving cell use different uplink-downlink (UL-DL)configurations, and each of the UL-DL configurations is information onwhich each subframe within a TDD frame is configured as an UL subframe,a DL subframe or a special subframe, wherein if a PHICH resourcecorresponding to the first UL data is not present in the subframe i, thenon-adaptive retransmission is not allowed in the second subframe of thesecond serving cell, wherein if an UL grant for the second subframe isreceived in the first serving cell, the UL grant for the second subframecomprising information indicative of whether or not the first UL data isto be retransmitted, wherein if the information indicative of whether ornot the UL data is to be retransmitted indicates retransmission, thefirst UL data is retransmitted in the second subframe, and wherein ifthe information indicative of whether or not the UL data is to beretransmitted indicates new transmission, a second UL data istransmitted in the second subframe.
 3. The method of claim 2, wherein ina case of a subframe in which the uplink grant for the second subframeis received in the first serving cell, the user equipment decodes onlythe uplink grant for the second subframe without attempting to receive aphysical hybrid-ARQ indicator channel (PHICH).
 4. The method of claim 2,wherein a subframe of the first serving cell in which the uplink grantfor the second subframe is received is any one of subframes indicated byD in a table below: UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 01 D D 2 D D D D D D 3 D D D D 4 D D D D D D 5 D D D D D D D D 6  .


5. User equipment, comprising: a Radio Frequency (RF) unit configured totransmit and receive radio signals; and a processor connected to the RFunit, wherein the processor is configured to: receive an uplink (UL)grant for a first subframe of a second serving cell through a firstserving cell, transmit UL data in the first subframe of the secondserving cell based on the UL grant, and perform a non-adaptiveretransmission for the UL data in a second subframe of the secondserving cell if a not-acknowledgement (NACK) for the UL data is receivedthrough a physical a hybrid automatic repeat request (HARQ) indicatorchannel (PHICH) in a subframe i of the first serving cell, wherein thefirst serving cell and the second serving cell use differentuplink-downlink (UL-DL) configurations, and each of the UL-DLconfigurations is information on which each subframe within a TimeDivision Duplex (TDD) frame is configured as an UL subframe, a DLsubframe or a special subframe, and wherein if a PHICH resourcecorresponding to the UL data is not present in the subframe i, thenon-adaptive retransmission is not allowed in the second subframe of thesecond serving cell.
 6. The method of claim 1, wherein if a UL grantindicating a retransmission of the UL data is received in the subframei, an adaptive retransmission for the UL data is performed in the secondsubframe of the second serving cell.
 7. The method of claim 1, whereinthe first serving cell and the second serving cell use two differentUL-DL configurations of UL-DL configurations 0-6 shown in a table below:DL-to-UL switch- UL-DL point Subframe n configuration periodicity 0 5 ms1 5 ms 2 5 ms 3 10 ms  4 10 ms  5 10 ms  6 5 ms  .


8. The method of claim 1, wherein the subframe i is a subframe locatedbetween the first subframe and the second subframe.
 9. The method ofclaim 1, wherein if a PHICH resource corresponding to the UL data and anUL grant are not present in the subframe i, the user equipment does notperform any UL transmission.